phil.shelton
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 posted on 21/2/03 at 07:26 PM |
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round tube chassis?
I am thinking of building a chassis from round tube to reasons
1 I think it could give a nice finish to the panels and 2 might be able to get it FREE
what problems do you think might a rise and has anyone else done it. also thinking of doing top and bottom side rails of chassis in one piece by using
a pipe bender
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philgregson
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| posted on 21/2/03 at 07:38 PM |
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There are several helpful discusions on this subject in the mid-engine section.
One is called something like -square or round tube?
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cymtriks
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| posted on 21/2/03 at 08:11 PM |
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From a construction point of view square tube is easier to use as it is easier to hold a square shape and cut an angle accurately than a round tube.
From a strength point of view round 1 inch tube will have about 3/4 the strength and stiffness due it having 3/4 of the cross sectional area. Using a
larger diameter round tube such as 1-1/4 (nearly equal to 1 inch square) or 1-3/8 (a bit stronger) will make up the difference. All this assumes that
the tubes being compared have the same wall thickness.
I wouldn't advise any reduction in chassis stiffness as the lowcost is not fully triangulated and is actually no better than a relatively simple
ladder type chassis of the same weight made of 4 x 2 inch RHS with 14 gauge wall.
There doesn't seem much point in a spaceframe that is significantly worse than a ladder frame but an awfull lot of kitcar spaceframes certainly fall
into this area.
I have posted the results of a stress analysis I made of the lowcost frame which showed how to double the chassis strength, reduce the number of
tubes, and reduce the weight by 10%. If you scroll back through this section you'll find it. If you want I'll e-mail it to you.
Good luck with your plans!
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Rorty
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| posted on 22/2/03 at 02:04 AM |
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Round tube is approximately 25% lighter and stronger than square tube of the same nominal size...lighter as it contains less metal than its square
counterpart, and stronger, as it resists beam and torsional loads better. It's a bit like an egg shell versus a pill box.
It does look cooler I'll admit, however, in the case of the Locost where you have a tight fitting body, you're not really going to see the round
tube chassis to its best effect. Fixing flat sheet panels directly to a round tube chassis is a pain in the proverbial, and can seldom be done neatly.
Remember, some of the sheet work on the Locost chassis is for structural purposes too.
I work with predominantly round tube chassis, but then none of the body panels are stressed items.
The Locost has such a basic chassis, it would be best left alone, with possibly the exception of the substitution of a few round tube braces,
strategically placed to help strengthen the structure.
If you can get a round tube chassis built for free, then surely it's possible to have the same bloke build you a square chassis for free? It would be
a different story if the reverse were the object!
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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jack nichs
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| posted on 22/2/03 at 09:21 AM |
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Hi Guys,
I've been watching the forum for some time with interest. Very informative!
Thought I might jump in here and correct an obvious stuffup.
The Moment of Inertia,I, of a square tube is greater than that of a round tube, so therefore, the square tube will ALWAYS be stronger and stiffer than
the round one, given that both have the same wall thickness.
Learned that in Mechanics lectures last month.
Cheers All.
Jack N.
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cymtriks
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| posted on 22/2/03 at 10:49 PM |
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I think that a point needs clearing up.
1 inch square is stiffer, due to the higher second moment of area values, in bending and stiffer in tension, due to the higher cross section, than 1
inch round of the same wall thickness.
However for the same weight for a given wall thickness the round tube will be stiffer in bending and in torsion.
Thus a 1 and 1/4 inch OD round tube has very nearly the same weight as a 1 inch square tube but will be slightly stiffer.
On another point the modifications I suggest for the lowcost actually make it simpler (less tubes), lighter and a lot stiffer (about double). The
really big factor in this is that the front of the lowcost chassis is seriously under triangulated and a very worthwhile improve ment can be made by
welding in diagonals between FU1 to LB and between FU2 and LA. Weld in a V brace from the ends of LD to the centre of LC. Weld in the panel between E
and LC (don't rivet in a sheet of alloy, the weight saving doesn't justify the drop in strength). Do chech that the new tubes will clear suspension,
steering and cooling system bits and pieces. That little lot is simple to add and increases the chassis stiffness by about 50%.
The rest of my mods involve changes to the transmission tunnel which save weight while further increasing stiffness.
Don't let people kid you about the stiffness of spaceframes versus ladder frames. The usual story assumes proper triangulation for spaceframes and
most of them simply aren't properly triangulated. Though no one has actually disputed this on this website I've took some flak for saying this on
other sites. Most spaceframes are actually no better than properly designed ladder frames of the same weight.
I was interested to see a reference to "last weeks lecture". I studied engineering at the university of Hull in England and I really enjoyed my time
there.
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Rorty
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| posted on 23/2/03 at 01:27 AM |
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I got it really ar$e about! 
Cymtrics is, of course, quite right. Weight for weight, round is stronger.
I was getting confused, as some racing bodies won't permit 1" square, but 1" round is OK, and so is 1 1/4" square!
I'm not an engineer, but I seem to remember it's something to do with "Young's modulus".
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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kb58
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| posted on 23/2/03 at 02:34 AM |
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Square tubing is easier to cut only if the tube will be in the same plane as the tube it's to mate with - a simple, single cut will do. Off axis is
another thing entirely, often involving 4 cuts (or more if other tubes intersect,) and not simple cuts that transverse all the way across the tube.
It become challanging to be sure, and ends up taking longer than using round tubing... especially if you use one of the tubing notchers for the round
stuff. Well worth the money IMO.
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James
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| posted on 24/2/03 at 09:51 AM |
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quote:
Originally posted by phil.shelton
I am thinking of building a chassis from round tube to reasons
1 I think it could give a nice finish to the panels and 2 might be able to get it FREE
what problems do you think might a rise and has anyone else done it. also thinking of doing top and bottom side rails of chassis in one piece by using
a pipe bender
Hi Phil,
I guess the look is a matter of personal taste but it may be worth you having a look at the difference between the Lolocost (round) and MK (square)
chassis.
Also, the 25mm square tubing is only gonna cost you £60 if you look around and maybe another £30 in 19mm. In the scale of spending the amount this
project is gonna cost you (remember the £250 is a load of BS- it's more like 10 times that amount! ) is this amount really relevent?
It's also a lot harder to attach all the little bits to round tube than square (all the little brackets and bits and pieces that you'll have to
attach to the chassis).
Anyway, just my two pence worth.
HTH,
James
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Rorty
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| posted on 25/2/03 at 01:59 AM |
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Cost wise, there shouldn't be much difference in building a chassis out of round tube.
James:
quote:
It's also a lot harder to attach all the little bits to round tube than square (all the little brackets and bits and pieces that you'll have to
attach to the chassis).
I beg to differ. It's a hell of a lot easier attaching brackets etc to round tube, especially on angles. Instead of having to go around all four
sides of a bit of square tube with a hacksaw, with round tube, you simply cut the angled joint with one fell cut of a holesaw. Job done!
Apart from the ease, any brackets so mounted on round tube, get a far better purchase than on square stuff. I've seen tabs pull out of the face of
square tube, and the exact same tab on a round tube chassis has stayed put for eternity.
But, if you don't have an electric drill and a holesaw.....
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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PerspexIt
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| posted on 25/2/03 at 08:43 AM |
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cut or bend?
Hi All,
you will make the chassis a standard chassis using round tubes instead square or you'll bend it? A1-D1 and F1 for example, can be the same tube as in
the Lolocost's chassis.
-P
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kingr
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| posted on 25/2/03 at 09:24 AM |
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But then why would you want to model your chassis on lolocost's? They seem too stingy/lasy to put a transmition tunnel in or use any sort of
triangulation, they use ERW for wishbones and worst of all, they make the robin hood.
Kingr
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PerspexIt
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| posted on 25/2/03 at 10:10 AM |
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No, no, no.. i dont want make a copy of the lolocost. Just have 1 tube instead of 3 seems good to me.
-P
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phil.shelton
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| posted on 26/2/03 at 08:02 PM |
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bends
I am looking at making the following tube sections as one there for reducing the number of welds
j2 and n2, f1 d1 and f2, Trans mition tunneltop tubes g c i and h d j
so if any one has an autocad drawing of chassis so i can work out the angles of bent.
also what do you think
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jcduroc
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| posted on 26/2/03 at 10:55 PM |
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quote:
Originally posted by Rorty
Cymtrics is, of course, quite right. Weight for weight, round is stronger.
I was getting confused, as some racing bodies won't permit 1" square, but 1" round is OK, and so is 1 1/4" square!
I'm not an engineer, but I seem to remember it's something to do with "Young's modulus".
So, Cymtrics, why not do it all (if no ally sheet riveting applies) in round tube, 1 1/4" for instance?
Joćo
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sg_frost
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| posted on 27/2/03 at 01:18 AM |
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Built mine out of tubular, cut with 25mm hole cutter in a pillar drill, looks realy good, even if i do say so myself.
+100mm wider
+2.8 V6
=Mental driver!!
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agree1sc
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| posted on 27/2/03 at 08:56 AM |
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RH Chassis
A friend of mine has told me that certain track day organiser will not allow Robin Hood owen to use their car due to it having a round Chassis. Does
any one know is this is correct?
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James
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| posted on 27/2/03 at 10:55 AM |
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quote:
Originally posted by Rorty
James:
quote:
It's also a lot harder to attach all the little bits to round tube than square (all the little brackets and bits and pieces that you'll have to
attach to the chassis).
I beg to differ. It's a hell of a lot easier attaching brackets etc to round tube, especially on angles. Instead of having to go around all four
sides of a bit of square tube with a hacksaw, with round tube, you simply cut the angled joint with one fell cut of a holesaw. Job done!
Apart from the ease, any brackets so mounted on round tube, get a far better purchase than on square stuff. I've seen tabs pull out of the face of
square tube, and the exact same tab on a round tube chassis has stayed put for eternity.
But, if you don't have an electric drill and a holesaw.....
I don't really understand how it can be easier- attaching something (say a piece of 3mm plate) to the flat face of a square tube must be easier than
the curved surface of a round tube where to get it stable you've got to 'fill in' with weld the acute angled gap behind the piece you're welding
to the tube.
But we may be talking a cross-purposes here anyway! 
Cheers,
James
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eddymcclements
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| posted on 27/2/03 at 01:36 PM |
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quote:
Originally posted by agree1sc
A friend of mine has told me that certain track day organiser will not allow Robin Hood owen to use their car due to it having a round Chassis. Does
any one know is this is correct?
I very much doubt that is the reason - much of the Caterham chassis is round tube and there are loads of them on track days.
Much more likely is that the track day organiser in question has something against Robin Hoods, or doesn't like the look of the chassis.
Cheers,
Eddy
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cymtriks
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| posted on 1/3/03 at 06:50 PM |
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Why not build it all in round tube?
As this question has been asked I can only think of one answer. It's your chassis, choose the tube type you are happiest working with. The
differences between 1 inch square and 1 and 1/4 inch round are fairly small from a real world structural point of view. From a personal point of view
I reckon square might be easier overall.
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